Update CSI Plugins README
Update CSI Plugins README

This patch updates the README for plugins for CSI 0.2.0.
It includes the following changes:
- Updates the CSC tool location
- Removes "get supported versions" because that was removed
  from CSI.

kubernetes-csi/csi-driver-nfs,kubernetes-csi/csi-driver-nfs,kubernetes-csi/csi-driver-nfs